StaticNekoX = Your profile icon needs to be a perfect square and exactly 200 pixels on each side, and it sounds like your image is a rectangle. (Your image program is probably trying to scale proportionally when resizing, so the one side doesn't end up looking squashed or stretched.)
You'll either need to crop some of the image to make the format a square shape -or- add a blank area to the side of the canvas if you want to preserve the portrait format of the entire image.